Recently, an augmented reality technology (an AR technology) has attracted attention in which a virtual object or various information items are synthesized or presented to an actual environment (or a part of the actual environment) as electronic information as additional information. In order to realize such an augmented reality technology, for example, a head mounted display is considered as a device presenting visual information. Then, in an application field, operation support in an actual environment is expected, and for example, route guidance information can be provided, or technology information with respect to an engineer performing maintenance can be provided. In particular, the head mounted display is extremely convenient since the display can be used without hands. In addition, even in the case of obtaining various information items or the like while moving the outdoors, it is possible to simultaneously capture both of various information items or the like configured of a video or an image and an external environment in a visual range, and thus, smooth movement can be performed.
In order for an observer to observe a two-dimensional image formed by an image forming device by a virtual image optical system as an enlarged virtual image, a virtual image display device (a display device) using a deflection unit including a hologram diffraction grating, for example, is known from Japanese Patent Application Laid-Open No. 2007-094175.
As a conceptual diagram is illustrated in FIG. 31, basically, an image display device 100′ includes an image forming device 111 which displays an image, a collimation optical system 112, and an optical device 120 in which light displayed on the image forming device 111 is incident and is guided to a pupil 21 of the observer. Here, the optical device 120 includes a light guide plate (a first substrate) 121, and a deflection unit which is disposed on the light guide plate 121. Specifically, the deflection unit is configured of a first diffraction grating member 141 and a second diffraction grating member 142 which include a reflective volume hologram diffraction grating film. Then, light exiting from each pixel of the image forming device 111 is incident on the collimation optical system 112, and a plurality of parallel light rays having different incident angles with respect to the light guide plate 121 are generated by the collimation optical system 112, and are incident on the light guide plate 121. The parallel light is incident from a second surface 121B of the light guide plate 121, and exits. On the other hand, the first diffraction grating member 141 and the second diffraction grating member 142 are attached onto a first surface 121A of the light guide plate 121, which is parallel to the second surface 121B of the light guide plate 121. Furthermore, for reference numerals representing other constituents in FIG. 31, refer to an image display device of Example 1 described with reference to FIG. 1. Then, in the image display device 100′, a virtual image is formed on the basis of the image, and thus, the observer is capable of observing the external image and the formed virtual image in a superimposed manner.
However, in the case of using the display device in the head mounted display, a reduction in weight is an extremely important factor. Therefore, as described in Japanese Patent Application Laid-Open No. 2007-094175, it is general that the deflection unit is configured of the hologram diffraction grating film which includes a photopolymer material.